Pipe joints or couplings – With casing – lining or protector – Lined
Reexamination Certificate
2002-02-26
2004-01-20
Nicholson, Eric K. (Department: 3679)
Pipe joints or couplings
With casing, lining or protector
Lined
C285S094000, C285S333000, C285S355000
Reexamination Certificate
active
06679526
ABSTRACT:
TECHNICAL FIELD
This invention relates to a threaded joint for an oil well type having excellent galling resistance. More particularly, it relates to a threaded joint for an oil well pipe used in the excavation of crude oil and which can undergo repeated tightening and loosening without using a liquid lubricant and without galling, which maintains air tightness, and which can be used repeatedly.
BACKGROUND ART
Oil well pipe such as tubing and casing which is used in the excavation of oil wells is typically connected by threaded joints. The depth of oil wells is normally 2,000 to 3,000 meters, but recently the depth has reached 8,000 to 10,000 meters in deep wells such as those in offshore oil fields. A threaded joint for connecting such oil well pipes is used under tensile forces in the axial direction caused by the weight of the oil well pipe and the threaded joint itself, a compound pressure due to internal and external surface pressure, and heat, so it is required that it be able to maintain air tightness without damage even in such an environment. Furthermore, during the process of lowering tubing or casing, there are cases in which a joint which is once tightened is loosened and then retightened. API (American Petroleum Institute) requires that there be no occurrence of seizing referred to as galling and that air tightness be maintained even if tightening (make-up) and loosening (break-out) are carried out ten times for a tubing joint and three times for a casing joint.
A threaded joint normally has a structure in which an external thread is formed on the end of an oil well pipe, an internal thread is formed on the inner surface of a threaded coupling, an unthreaded metal contact portion formed on the end of the external thread is mated with an unthreaded metal contact portion formed on the base of the internal thread, and by performing tightening, the unthreaded metal contact portions are made to contact each other and a metal seal portion is formed. Galling resistance and air tightness are increased by performing surface treatment of the threads and the unthreaded metal contact portions and by applying a compound grease at the time of tightening.
However, particularly in the unthreaded metal contact portions, a high surface pressure acts which exceeds the yield point of the material of the threaded joint, so that galling easily takes place. Thus, various threaded joints have been proposed for improving galling resistance in such portions.
For example, Japanese Published Unexamined Patent Application Sho 61-79797 discloses a threaded joint in which the threaded portions are plated with Zn, Sn, or the like, and the unthreaded metal contact portions are plated with gold, platinum, or the like.
Japanese Published Examined Patent Application Hei 3-78517 discloses a pipe joint on which is formed a film of a synthetic resin containing 20-90% of molybdenum disulfide having a particle diameter of at most 10 micrometers dispersed therein.
Japanese Published Unexamined Patent Application Hei 8-103724 discloses a surface treatment method for a steel pipe joint in which a resin film containing molybdenum disulfide is formed atop a manganese phosphate chemical formation coating.
Japanese Published Unexamined Patent Application Hei 8-105582 discloses a surface treatment method for a pipe joint in which a nitriding treatment layer is made a first layer, an iron plated layer or an iron alloy plated layer is made a second layer, and atop this is formed a third layer comprising a resin film containing molybdenum disulfide.
However, the threaded joints disclosed in the above-described publications are each premised on the use of a compound grease. This grease contains powders of heavy metals such as zinc, lead and copper, and there is the concern of the occurrence of environmental pollution when a situation develops such as the grease which is applied at the time of joining the threads being washed off or the grease overflowing to the outer surface at the time of tightening. In addition, the process of applying a compound grease worsens the working environment and also decreases the operating efficiency. Accordingly, there is a desire for the development of a threaded joint which does not use such a compound grease.
A threaded joint in which a solid lubricant film is formed on its surface has been proposed as a threaded joint which does not use a compound grease.
For example, Japanese Published Unexamined Patent Application Hei 8-233163, Japanese Published Unexamined Patent Application Hei 8-233164, and Japanese Published Unexamined Patent Application Hei 9-72467 disclose threaded joints having formed thereon a resin film in which molybdenum disulfide is dispersed in a resin.
However, a threaded joint having a resin film formed thereon has the problem that compared to when a compound grease is used, the coefficient of friction of the contacting surfaces is high at the time of tightening the threaded joint, and a large tightening force becomes necessary. In the assembly of an oil well pipe line, it is important to reduce the tightening force of the threaded joint in order to improve workability, and in order to accomplish this, a threaded joint having a low coefficient of friction at contacting surfaces and excellent lubricity is desired as a threaded joint not using a compound grease.
In recent years, there has been a demand for a heat resistant threaded joint for use in high temperature oil wells in which the environment of use has been a high temperature of 250-300° C., and for steam injection oil wells in which high temperature steam (350° C.) which may even reach the critical temperature is injected in order to increase the crude oil recovery efficiency. Accordingly, a threaded joint is desired to have the properties that after a heat resistance test is performed on a tightened joint at a temperature exceeding 350° C., air tightness is maintained even when loosening and retightening is carried out.
However, with conventional technology disclosed in publications like those described above, it is difficult to guarantee such performance.
Namely, when a threaded joint is tightened, when a compound grease like that specified in API Standard BUL5A2 is employed, the grease component vaporizes due to the high temperature, and lubricity decreases, so there is the problem that a prescribed air tightness cannot be obtained at the time of retightening after loosening. Accordingly, the technology disclosed in Japanese Published Unexamined Patent Application Hei 5-117870, Japanese Published Unexamined Patent Application Hei 6-10154, Japanese Published Unexamined Patent Application Hei 5-149485, Japanese Published Unexamined Patent Application Hei 2-085593, and the like, which is premised on the application of a compound grease, has problems with respect to maintaining air tightness at high temperatures.
In the technology which is disclosed in Japanese Published Unexamined Patent Application Hei 8-233164 and Japanese Published Unexamined Patent Application Hei 9-72467, which is characterized in that it does not use compound grease, the resin deteriorates when it is exposed for long periods to a high temperature which may reach as high as 400° C., so it fails to function as a binder holding a solid lubricant such as molybdenum disulfide, and there are problems that the lubricity decreases, improper tightening and galling occur, and air tightness worsens.
In this manner, at present, a threaded joint having excellent galling resistance which can be repeatedly used under high temperature conditions reaching as high as 400° C. has not been obtained.
Furthermore, a threaded joint which is disclosed in the above-described publications and which does not use a compound grease has the problem that the tightening torque easily varies and tightening is unstable compared to a threaded joint using a compound grease. In addition, with threaded joints of the above-described publications which do not use a compound grease, the effect of preventing rusting of the joint in the period between shipment from a factory a
Nakasuji Kazuyuki
Yamamoto Hideo
Clark & Brody
Nicholson Eric K.
Sumitomo Metal Industries Ltd.
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